In an article transport facility provided with ceiling or overhead transport vehicles that travel along a railed track, a travel obstructing device for obstructing travel of a ceiling transport vehicle in order to ensure a worker's safety when performing maintenance work, for example, is used by placing the travel obstructing device on the railed track at a location upstream of the location (work location) at which work is performed. Generally, a ceiling transport vehicle travels while obtaining information on a distance to any obstacle located ahead by means of a sensor installed to its main body and is configured to stop automatically when the distance is less than or equal to a reference distance specified in advance. A travel obstructing device functions as an obstacle to a ceiling transport vehicle when it is placed on the railed track, to cause a ceiling transport vehicle approaching the work location to stop.
Examples of such travel obstructing devices are disclosed in JP Publication of Application No. 2002-19605 (Patent Document 1) and JP Publication of Application No. 2015-209185 (Patent Document 2). The travel obstructing devices disclosed in the references identified above are designed only from a viewpoint of ensuring a worker's safety. And additional arrangements are made to allow a worker to install such device by himself or herself, and to increase its strength.
However, for example, while a worker is working (e.g., performing maintenance work) with a travel obstructing device placed on the railed track, another worker may start working at a location further downstream. And in such a situation, the second worker who started working at the downstream location after the first worker may proceed with the work without placing a travel obstructing device for himself/herself, believing that the obstructing device already placed by the first worker upstream would be sufficient. In such a situation, if the first worker who finished work at the upstream location removes the travel obstructing device without notifying the second worker working downstream, any ceiling transport vehicle that was caused to be at rest until then would start to move, and may reach the work location located downstream at a predetermined speed. Of course, this would not happen if the second worker at the downstream location who started working after the first worker took a precautionary measure of placing a travel obstructing device for himself or herself. It would be preferable, from a viewpoint of improving safety of the entire facility, to have a mechanism in place that would makes it easier for a worker to become aware of the possibility that there can be an approaching ceiling transport vehicle even if such a precautionary measure is not taken. In that respect, improving safety in a situation where a number of workers work simultaneously was not considered in either Patent Document 1 or Patent Document 2.